Standardized containers have long been used to great advantage for the transportation of goods. At their corners, these containers have facilities, referred to as container corners or twist blocks, that project beyond the sides of the container therebetween by a certain amount. Said container corners are designed in such a way that standardized holders can engage with and be locked into said container corners.
Goods of large volume (referred to hereinafter as unit loads) cause substantial problems during handling or transportation when they are unsuitable for containerized transport, for example on account of their dimensions and/or weight. Such unit loads can be steel towers or tower segments, for example, which must often be transported as supports for telecommunications facilities or wind turbines. Such sections are usually 11-25 meters in length, up to 4 meters in diameter and between 20-70 tons in weight. These figures may even be exceeded.
In the following, the invention and the problems encountered in the prior art are described with reference to such steel tower segments. However, attention is expressly drawn to the fact that the invention is not confined to such applications and that it essentially relates to any kind of unit load.
As is well known, steel tower sections present a series of handling and transportation tasks, beginning with manufacture and continuing through transportation to the construction site and to erection of the edifice.
Both ends of the mostly circular cylindrical tower segments are usually fitted with flanges with which the separate sections are connected during erection. Said flanges are also used in most cases to attach the handling or transportation means to the section.
Such means are rotary adapters, for example, by means of which the sections horizontally aligned along their longitudinal axis can be turned about their longitudinal axis, in order, for example, to perform paint finishing work at any part of the outer wall. These rotary adapters are fastened with screws to the flanges.
By this method, for example, feet are screwed onto the flanges to enable the section to be stored with a predetermined clearance from the ground. As soon as the feet are attached and the section has been laid down, the rotary adapters are removed. The feet are positioned in such a way that there is a certain probability that they still fit and do not have to be refitted when the section is later transported by truck.
When the sections are smaller, they can be transported by truck on a low loader.
However, a so-called boiler bridge is required in the case of larger sections. Such a boiler bridge comprises a traction unit with a low loader mounted thereto and a rear trailer, said low loader and trailer being connected to each other by spars and the gap between the two being adjustable within certain limits. When a section is transported using the boiler bridge, on the other hand, different feet must be screwed onto the section in order to hold it in a certain position on the spars of the boiler bridge.
As soon as the section reaches the construction site, hoisting brackets are screw-fastened to the flange of the segment that is to be set upright for assembly. As soon as the section has been raised using the hoisting brackets, the feet are removed from the flange, and the section can be fitted into the tower.
If part of the transportation route is by sea, the feet attached to the section can be welded to the deck of the ship. The feet have to be changed again if the section was transported to the port using a boiler bridge. Although welding the feet is both a simple and effective way of securing the section for transportation, it harbors the risk of the section being damaged when the cargo is discharged—especially when the feet are not separated from the deck of the ship, but simply screwed off the flanges of the section instead. What is more, the feet that are then missing or destroyed have to be replaced by new ones in order to transport the section by truck from the port to the construction site.
As an alternative to welding the feet to the deck of the ship, the sections are secured by chains, for example, which are fed either through the holes in the section or around the outside of the section and then made fast. In order to hold the heavy section in a reliable way, the chains are tightly lashed. This can easily lead to deformations in the section, or damage to the coating, for example. If a boiler bridge is ready for use in the destination port, it is necessary to change the feet once again.
Well known devices are integral elements with two portions, one of which is for fastening the device to the unit load and the other for operation during handling (e.g., hoisting or laying down).
In the devices described, the frequent, time-consuming and hence cost-intensive refittings for the various carrying, support and hoisting procedures during handling of the section in the manufacturing process and during transportation are severe disadvantages. Each device is essentially designed for one task only and for one function only.
One transportation variant on land is a so-called transportation cross. The latter comprises a traction unit and a trailer. The linkage between the two vehicles is provided by the item to be transported—i.e., the tower section, for example. Holding devices that can be screwed to the flanges of the section are disposed on the traction unit and on the trailer.
Assembly and disassembly of the section between the traction unit and the trailer takes a disadvantageous 2.5 to 3 hours in each case, during which time the section must be held by a crane. Use of both the crane and the personnel required is therefore blocked for a very long time.